The present invention relates generally to the evaluation of heart rate variability, and specifically to the analysis of the power spectrum distribution thereof.
With the growing complexity of life, the relation between physiological conditions and emotional health becomes of increasing interest. Many studies have shown that stress and other emotional factors increase the risk of disease, reduce performance and productivity and severely restrict the quality of life. To this end, the medical communities around the world continually seek remedies and preventive plans. Recently a focus on the self-regulation of systems within the body has led to research in the areas of biofeedback, etc.
In the last 25 years, a variety of new techniques have been introduced as alternatives to more traditional psychotherapies or pharmaceutical interventions for improving mental and/or emotional imbalances. In addition to the more psychological approaches like cognitive re-structuring and neurolinguistic programming, psychologists have employed several techniques from Eastern cultures to xe2x80x9cstill the mindxe2x80x9d during focused meditation. In yoga, for example, one generally focuses on the breath or parts of the brain, whereas in qigong one focuses on the xe2x80x9cdan tienxe2x80x9d point (below the navel). In a Freeze Frame(copyright) (FF) technique, developed by the Institute of Heart Math in Boulder Creek, Calif., one focuses attention on the area around the heart. All these techniques focus attention upon areas of the body which are known to contain separate but interacting groups of neuronal processing centers, and biological oscillators with which they interact. The heart, brain, and the intestines contain biological oscillators known as pacemaker cells. By intentionally focusing attention on any one of these oscillator systems, one can alter its rhythms. This is at least true for the brain (meditation), yogic breathing (respiration), the heart (FF), and most likely the gut (qigong), since it is also regulated by the autonomic nervous system (ANS). The body also contains other oscillating systems such as the smooth muscles of the vascular system. We have previously shown that this system, measured by recording pulse transit time (PTT), as well as the brain, measured by an electroencephalograph (EEG), the heart, measured by a heart rate variability (HRV), and the respiration system, measured by the respiration rate, can all entrain. Furthermore, they all synchronize to a frequency varying around 0.1 Hertz (Hz). Thus, one can intentionally bring these systems, acting as coupled biological oscillators, into synchronize with each other.
The FF technique is a self-management technique by which one focuses on the heart to disengage from moment-to-moment mental and emotional reactions. A study utilizing the FF technique in a psychological intervention program with HIV-positive subjects resulted in significant reductions in life-stress, state and trait anxiety levels, and self-assessed physical symptoms. Two other studies with healthy individuals using the FF technique to enhance positive emotional states showed increased salivary IgA and increased sympathovagal balance. Increased sympathovagal balance is known to protect against detrimental physiological effects associated with overactive sympathetic outflow from the brain. Other studies have shown the techniques to be effective in improving autonomic balance and decreasing the stress hormone cortisol and increasing DHEA, improving glycemic regulation in diabetics, reducing blood pressure in hypertensive individuals and significantly reducing psychological stressors such as anxiety, depression, fatigue and overwhelm in many diverse populations.
Sympathovagal balance has been measured using various techniques. For example, individuals can be trained to consciously control their heart rate using biofeedback techniques. However, the enhanced parasympathetic activity is probably mediated through control of respiration. Neutral hypnosis and operant conditioning of heart rate have been demonstrated to decrease in the sympathetic/parasympathetic ratio by increasing parasympathetic activity independent of controlled breathing techniques. The FF technique does not require biofeedback equipment nor does it require conscious control of respiration although a short breathing protocol is used this technique. Our results suggest that emotional experiences play a role in determining sympathovagal balance independent of heart rate and respiration. The shifts in sympathovagal balance toward increased low-frequency (LF) and high frequency (HF) power (measures of heart rate variability) were physiological manifestations of experiencing the emotional state of appreciation. The FF technique focuses on genuinely experiencing the feelings of sincere appreciation or love, in contrast to visualizing or recalling a previous positive emotional experience.
The results of our studies indicate that relatively short periods of practice of the FF technique and other tools developed by the Institute of HeartMath leads to either an xe2x80x9centrainmentxe2x80x9d or xe2x80x9cinternal coherencexe2x80x9d mode of heart function (described in greater detail below). Most subjects who are able to maintain these states report that the intrusion of random thoughts is greatly reduced and that it is accompanied by feelings of deep inner peace and heightened intuitive awareness.
We also observed that positive emotional states, which lead to the entrainment mode, generated marked changes in the dynamic beating patterns of the heart. A method for quantifying and analyzing and quantifying these heart rhythms is called analysis of heart rate variability (HRV). The normal resting heart rate in healthy individuals varies dynamically from moment to moment. Heart rate variability, which is derived from the electrocardiogram (ECG) or pulse, is a measure of these naturally occurring beat-to-beat changes in heart rate and is an important indicator of health and fitness. HRV is influenced by a variety of factors, including physical movement, sleep and mental and activity, and is particularly responsive to stress and changes in emotional state. The analysis of HRV can provide important information relative to the function and balance of the autonomic nervous system, as it can distinguish sympathetic from parasympathetic regulation of heart rate. Decreased HRV is also a powerful predictor of future heart disease, increased risk of sudden death, as well as all-cause mortality.
Frequency domain analysis decomposes the heart rate tachogram or waveform into its individual frequency components and quantifies them in terms of their relative intensity, in terms of power spectral density (PSD). By applying spectral analysis techniques to the HRV waveform, its different frequency components, which represent the activity of the sympathetic or parasympathetic branches of the autonomic nervous system, can be discerned. The HRV power spectrum is divided into three frequency ranges or bands: very low frequency (VLF), 0.033 to 0.04 Hz; low frequency (LF), 0.04 to 0.15 Hz; and high frequency (HF), 0.15 to 0.4 Hz.
The high frequency (HF) band is widely accepted as a measure of parasympathetic or vagal activity. The peak in this band corresponds to the heart rate variations related to the respiratory cycle, commonly referred to as respiratory sinus arrhythmia. Reduced parasympathetic activity has been found in individuals under mental or emotional stress, suffering from panic, anxiety or worry and depression.
The low frequency (LF) region can reflect both sympathetic and parasympathetic activity, especially in short-term recordings. Parasympathetic influences are particularly present when respiration rates are below 7 breaths per minute or when an individual takes a deep breath. This region is also called the xe2x80x9cbaroreceptor rangexe2x80x9d as it also reflects baroreceptor activity and at times blood pressure wave activity and resonance.
When an individual""s HRV pattern and respiration are synchronized or entrained, as can happen spontaneously in states of deep relaxation, sleep or when using techniques to facilitate autonomic balance such as Freeze-Frame and the Heart Lock-In, the frequency at which the entrainment occurs is often near 0.1 Hertz. This falls in the center of the LF band and could be misinterpreted as a large increase in sympathetic activity, when in reality it is primarily due to an increase in parasympathetic activity and vascular resonance. Sophisticated modeling techniques have shown that in normal states, about 50% of the total power in the LF band is explained by neural signals impinging on the sinus node which are generated at a central level, and the majority of the remaining power is due to resonance in the arterial pressure regulation feedback loop. The sympathetic system does not appear to produce rhythms that appear much above frequencies of 0.1 Hz, while the parasympathetic can be observed to operate down to frequencies of 0.05 Hz. Thus, in individuals who have periods of slow respiration rate, parasympathetic activity is modulating the heart rhythms at a frequency that is in the LF band. Therefore, in order to discriminate which of the ANS branches is pumping power into the LF region, both respiration and PTT should be simultaneously recorded and considered.
The increase in LF power while in the entrainment mode may represent increased baroreceptor afferent activity. It has been shown that the LF band reflects increased afferent activity of baroreceptors. The LF band has indeed been shown to reflect baroreceptor reflex sensitivity and is affected by physiological states. Increased baroreceptor activity is known to inhibit sympathetic outflow from the brain to peripheral vascular beds, whereas stress increases sympathetic outflow and inhibits baroreflex activity. The increase in LF power seen during the state of deep sustained appreciation may have important implications for the control of hypertension, since baroreflex sensitivity is reduced in these individuals.
There is a noticeable and obvious transition after the FF intervention to the entrainment mode which can be seen in the HRV waveforms and PSD data. In addition, many subjects report that they are able to use the FF technique while they were in a xe2x80x9ctensexe2x80x9d conversation with someone and starting to react. Even in these conditions, the HRV waveforms indicate that they were able to shift to and maintain the entrainment state.
From tachogram data, it can be seen that, as one moves from a state of frustration to one of sincere appreciation a transition occurs in the waveforms from a noisy wave of large amplitude to a non-harmonic wave form of similar amplitude (entrainment). We have also identified an additional state we call xe2x80x9camplified peacexe2x80x9d to indicate this special emotional state of very deep peace and inner harmony. In this state, the HRV waveform becomes a smaller amplitude wave (internal coherence). In general, the transition in the frequency domain (PSD) is from a wide-band spectrum of moderate amplitude to a narrow-band spectrum around 0.1 Hz of very large amplitude (entrainment) and then to a wide-band spectrum of very small amplitude (internal coherence).
In most individuals, small to near-zero HRV, as just described, is an indicator of a potentially pathological condition or aging because it connotes loss of flexibility of the heart to change in rate or a decreased flow of information in the ANS. However, in trained subjects, it is an indication of exceptional self-management of their emotions and autonomic nervous system because their HRV is normally large and the shift into the internal coherence mode is a result of intentionally entering the amplified peace state. This is very different from a pathological condition underlying lowered HRV (in such cases the HRV is always low). The connection between emotional states and HRV could possibly account for the occasional observation of low HRV in otherwise healthy individuals which has detracted from the clinical utility of HRV analysis for unequivocally predicting disease.
During the condition of internal coherence, the electromagnetic energy field produced by the heart, as seen in a fast Fourier transform (FFT) analysis of an electrocardiogram (ECG) signal, is a clear example of a coherent electromagnetic field. Recent advances in the understanding of the interaction between coherent signals and noise in nonlinear systems has resulted in the prediction that these nonthermal, coherent electromagnetic signals may be detected by cells. Further evidence suggests that coherent electromagnetic fields may have important implications for cellular function. For example, it has been recently demonstrated that nonthermal, extremely low frequency electromagnetic signals may affect intracellular calcium signaling. In addition, coherent electromagnetic fields have been shown to produce substantially greater cellular effects on enzymatic pathways, such as ornithine decarboxylase activity, than incoherent signals. This fact suggests that the state of internal coherence may also affect cellular function and provides a potential link between emotional states, autonomic function, HRV and cellular processes.
Conscious focus of attention and/or positive emotions has been shown to significantly influence HRV and PSD. The results of our research support previous work and suggest that psychological interventions which minimize negative and enhance positive emotional states may significantly impact cardiovascular function.
The results of work in this area demonstrate that sincere feelings of appreciation produce a power spectral shift toward LF and HF activity and imply that 1) the major centers of the body containing biological oscillators can act as coupled electrical oscillators, 2) these oscillators can be brought into synchronized modes of operation via mental and emotional self-control, and 3) the effects on the body of such synchronization are correlated with significant shifts in perception and cardiovascular function. It is suggested that positive emotions lead to alterations in sympathovagal balance which may be beneficial in the treatment of hypertension and reduce the likelihood of sudden death in patients with congestive heart failure and coronary artery disease.
There is a need to provide quantified information regarding the balance of the ANS which is easily used and does not require extensive biofeedback equipment. There is further a need for a mobile method of monitoring this balance for use in everyday life.